The present invention pertains generally to signal generators and more particularly to high frequency, wideband harmonic signal generators. Signal generators of this generic type have previously used a number of narrow frequency range oscillators which provide a wide frequency range by switching between the oscillators for each narrow frequency band. Stable power output and smooth frequency generation have been difficult to achieve in this type of wideband signal generator.
Another type of wideband generator has utilized an oscillator-multiplier approach which selects various harmonic frequencies of a single oscillator. When this approach has been used, complicated and unreliable methods of compensating for tuning nonlinearities have been resorted to. Typically, diode function generators have been relied upon to compensate for the tuning nonlinearities, but the unreliability of this method of compensation is inherent. This unreliability stems from temperature variations and inherent hysteresis of the yittrium iron garnate (YIG) oscillator and YIG multiplier, which together cause tracking alignment problems resulting in excessive power variations across the frequency range. In an attempt to attain leveled output power versus frequency, previous devices have used automatic level loops consisting of pin diode attenuators, directional couplers, crystal detectors and amplifiers. These devices, however, have been expensive to implement and have generally not provided the desired result, i.e., constant output power across the frequency range from 1 to 18 GHz.